Circuit configuration for processing the output signals of a speed sensor to eliminate noise

ABSTRACT

A circuit configuration for editing, or processing the output signal of a speed sensor (5) includes a trigger circuit (1, 22), the changeover points or &#34;hysteresis&#34; of which are controllable, with the circuit configuration being furnished with circuits for determining the coupling factor (k), and with circuits for adjusting the hysteresis in response to the coupling factor. The coupling factor (k)--multiplied by the frequency of the sensor signal corresponding to the speed--forms the amplitude of the sensor output signal. With the coupling factor (k) being high, the hysteresis will be high, while it will be low with a low coupling factor.

FIELD OF THE INVENTION

The present invention is concerned with a circuit configuration forediting, or processing the output signal of a speed sensor, thefrequency of which is evaluated for determining the speed, with theamplitude being equally dependent on the speed. Speed sensors of thistype are needed, for example, in anti-locking control systems (ALC) orin traction slip control systems (TSC).

BACKGROUND OF THE INVENTION

DE-OS German 32 34 637 teaches a circuit configuration of theafore-described type, by which the sensor signals are edited for anelectronic anti-locking system. The information on the wheel rotatingpattern required for the control is obtained with the aid of sensorsignals. For this purpose, a toothed disc rotates along with the wheel,with the disc cooperating with a stationary inductive transducer. Theoutput signal of the inductive transducer is available in the form of ana.c. voltage which in frequency and amplitude is proportional to thewheel speed. With the aid of a trigger circuit, the sensor signals areedited, i.e. boosted and converted into a square wave signal or a pulsesequence, the frequency of which corresponds to the speed. The triggercircuit, in addition, contains filters to attenuate noise signals to theextent possible.

The heavy dependence of the amplitude on the speed results in that, atlow wheel speeds, the output signals will become so weak that they canonly be distinguished from the inevitable noise signals by takingadditional steps. Moreover, because the voltage induced in thetransducer is greatly dependent on the air gap between the transducerand the toothed disc and, hence, on the operating tolerances,eccentricities of the wheel or the positioning of the wheel, the outputsignal, for identical wheel speeds, can assume highly differentamplitudes. In adverse circumstances, i.e. at a low speed and a largeair gap, the output signal may become extremely weak. This also appliesif, through costly correcting and adjusting efforts, the mechanicaltolerances are kept low.

Another process and circuit configuration for editing the sensor outputsignals have been described in DE-OS German 35 43 058, which isconcerned with an enhanced separation of noise signal and useful signal.For that purpose, two low-pass filters are provided between the sensoroutput and the trigger circuit, which generate a useful signal on theone hand, and a reference signal on the other hand. The two signals arecompared. In response to the difference of the two signals, with the aidof a comparator, a pulse-shaped output signal, viz. the edited sensorsignal, is generated. The reference signal, with the aid of a controlsignal obtained through a matching circuit, dynamically follows theuseful signal.

The strong dependence of the amplitude of the output signal of thesensor on the speed and on the air gap between the transducer and thetoothed disc does, however, still renders difficult the layout of atrigger circuit of this type. The response threshold, underconsideration of the largest air gap permitted in the tolerance range,and under consideration of the lowest speed to which the controllerresponds, will have to be rather low, such as 100 mV, so that thetrigger circuit in such an extreme case will reliably respond. In theevent of an air gap which is small by accident or by the toleranceconditions, and a resultant relatively strong noise signal, there will,however, be danger for the trigger threshold to be reached also by thenoise signal. The prior known grinding of the tires along the roadcausing so called "frictional vibrations", the dynamic changes in theair gap as a result of roadway shocks and numerous other causes createnoise signal levels exceeding the response threshold designed for thelower limit range.

SUMMARY OF THE INVENTION

The problem underlying the invention, therefore, resides in overcomingthe disadvantages described and in providing a circuit configurationwhich, on the one hand, sensitively responds to useful signals andnevertheless does not respond to noise signals of the type describedthat occur in practice.

This problem can be solved by a circuit configuration of theafore-mentioned type which substantially comprises a sweep circuit ortrigger circuit, the switch-over points or "hysteresis" of which arecontrollable. Also included are circuits for determining a couplingfactor which, multiplied by the frequency of the sensor signalcorresponding to the speed, is the amplitude of the output signal of thesensor. Further included are circuits for adjusting the hysteresis ofthe trigger circuit in response to the coupling factor.

Because of the automatic computation of the coupling coefficient and thecorresponding adjustment of the hysteresis, the trigger threshold willbe high, for example, for an accidentally small air gap resulting bothin high useful signals and in relatively high noise signals at theoutput of the sensor. Conversely, in the event of a large air gapweakening both the useful signals and the noise signals, the responsethreshold of the trigger is low. Hence, the inevitable tolerances ofassembly of the sensor are offset by adaptation of the trigger circuitand the hysteresis of the trigger circuit, respectively. As the couplingfactor, in one example may fluctuate at a ratio of 1:20 (i.e. between 3and 60 mV/Hz), the adaptation is extremely important to the suppressionof noise signal effects. The signal-to-noise ratio may be raised byalmost the same factor.

The adaptation of the hysteresis to the coefficient of coupling assuggested by the invention results in savings in the sensor and theassembly thereof. Compared to traditional solutions, enhanced assemblytolerances are achieved. Less strict requirements are placed upon thesignal transmission between the sensor and the electronic unit, becauseof the lower effect of noise signals. Avoidance of or substantialreduction in trigger errors will result in an enhanced control qualityof the anti-locking or traction slip control system.

According to a preferred embodiment of the invention, the hysteresis ofthe trigger circuit is adjusted to the amplitude of the signal Whichprevails at the output of the sensor at the lowest speed to bedetermined.

Moreover, the circuit configuration may be so designed that thehysteresis, with an increasing speed or frequency, rises continuously orby increments. The dependence can be so selected that the ratio betweenthe permitted noise level and the useful signal, throughout the speedrange, remains approximately constant.

In another preferred embodiment of the invention, the influence of thecoupling factor on the hysteresis rise is weighted or varied in responseto the rising frequency of the sensor signal and to the speed of anautomotive vehicle, based upon the occurrence of a predeterminedregularly recurring event, such as actuation of the ignition. At arelatively low speed, the probability that the coupling factor wasproperly identified is lower than at a higher speed, so that the circuitconfiguration, feasibly, is so designed that the influence of thecoupling factor on the hysteresis rise increases with a rising speed andfrequency, respectively, of the output signal of the sensor continuouslyor in several steps. In case of a decrease in the speed of theautomotive vehicle the stronger influence on the hysteresis speed ismaintained. It is only after the next ignition actuation that theinfluence of the coupling factor on the hysteresis rise is againincreased stepwise or continuously.

Further features, advantages and applications of the invention willbecome apparent from the following illustration with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a circuit configuration according tothe invention, and

FIG. 2 is a block diagram of an embodiment of the circuit configurationaccording to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

According to FIG. 1, the circuit configuration of the invention,basically, consists of a sweep circuit or trigger circuit 1 of avariable controllable hysteresis, a circuit 2 for computing the couplingfactor k, and another circuit 3 for computing the hysteresis and thechangeover contacts of the trigger circuit 1 in response to thedetermined actual coupling factor k, and for generating a signaldetermining the operating point and the hysteresis of the triggercircuit 1. The output signal of a wheel sensor 5 will be edited with theaid of this circuit configuration. A rectangular-wave signal or a pulsesequence, the frequency or pulse ratio of which is a measurement for thespeed, will be derived from this sensor signal. The frequency andamplitude of the rectangular-wave signal are dependent on the wheelspeed, and the rectangular-wave signal is made available at the outputTA of the circuit. The signal on output TA is substantially cleared fromnoise or misinformation and can be reprocessed, for example, in theelectronic controller of an anti-locking control system (not shown).Thus, this rectangular-wave signal at output TA is an edited version ofthe output signal from a speed sensor, and serves as a control signal tobe inputted to an anti-locking control system.

FIG. 2 shows an embodiment of the invention according to FIG. 1.

The signal of the wheel sensor available on output A₁ of the wheelsensor 5, with the aid of a comparator 6, a forward/backward counter (orup/down counter) 7 and a digital-to-analog converter 8, is firstconverted into a digital electronically reprocessed signal. Depending onthe condition of the output signal (high or low) of the comparator 6which, in turn, is determined by the difference of the two input signalsof the comparator, the counter 7 counts either forward or backward. Theworking cycle for this counter and for the other components of thecircuit shown in FIG. 2 is provided by a clock generator 9, thefrequency of which can be scaled down by a divider 10, should this berequired. In one embodiment of the invention, the clock generatorfrequency was 60 kHz and, by stage 10 was reduced to 30 kHz. The countat the output A₃ after conversion into an analog signal bydigital-to-analog converter 8 is compared to the sensor output signalA₁.

Moreover, count A₃, through a multiple line 11, e.g. an 8-bit data line,is communicated to comparators 12, 13 to be compared therein, on the onehand, with the stored maximum value (in comparator 12) and, on the otherhand, with the stored minimum value (in comparator 13) of the count.Such maximum and minimum values, respectively, are formed in memories14, 15 the inputs of which, equally are in communication with the dataline 11. Through an AND-gate 16 also in communication with the operationcycle and synchronizing the work sequence, the memory contents of themaximum memory 14 are increased if count A on the input of thecomparator 12 exceeds the stored maximum value communicated to thesecond input B of the comparator 12. The memory contents of the minimummemory 15 are correspondingly adjusted if the value on the input A ofthe comparator 13 is less than the stored minimum value communicated tothe second input B of the comparator 12.

The output signals of the maximum and of the minimum memories 14 and 15,respectively, are supplied to an adder 18 to determine the average valueof the output signal of the sensor. The output of the adder 18 leads toan add-substract circuit 19 adding to or subtracting from the averagevalue a value representing the computed "hysteresis" so that,eventually, the value of the output of this circuit 19, dependent on theaverage value and the computed hysteresis, after conversion into acorresponding analog value with the aid of a digital-to-analog converter21, will fix the operating point of a trigger circuit 22 correspondingto the trigger circuit 1 according to FIG. 1. The output signal of theadder 18 representing the average value, moreover, will be returned tothe memories 14, 15. The second input signal of the trigger circuit 22is the output signal A₁ of the sensor 5. The level at the input A of thetrigger circuit 22, precisely speaking, does not form the point ofoperation (the work point) but rather the point of operation±hysteresis.Available at the output TA of the trigger circuit 22 is the editedsignal of the wheel sensor 5. It is a rectangular-wave signal which,optionally, can be converted into a pulse sequence.

Moreover, the maximum and minimum counts, in each positive flank of theoutput signal TA of the trigger circuit 22, are stored in the memorycircuits 23, 24. The amplitude of the sensor signal can then bedetermined with the aid of a differential generator 25. In each positiveflank of the correction signal TA, in addition, the maximum count inmemory 14 is reduced to the average value.

In each negative flank, the minimum count in memory 15 is restored tothe average value. This will be needed to detect the actual amplitudeand the average value.

This amplitude of the sensor signal in response to the speed and thefrequency, respectively, corresponding to the said speed enables thecomputation of the coupling factor, k, according to the formula

    k=U.sub.sensor /f

where U_(sensor) is the amplitude of the sensor signal and f is themeasuring frequency at a tooth number of the sensor wheel (not shown) ofabout 50, being approximately between 30 and 2000 Hz, this relating to awheel sensor for an anti-locking system for use with automotivevehicles.

In the practice of the invention, the hysteresis and the switchoverpoints of the trigger circuit 22 (and 1 in FIG. 1, respectively) arefixed in response to the coupling factor.

The sensor amplitude determined in the differential generator 25, withthe aid of a divider circuit 26, is related to and weighted with thewheel speed or the frequency corresponding to the wheel speed. Theoutput signal of this divider circuit is stored in a memory 20 and--asprevious described--is reprocessed in circuits 19 and 21 for work pointdetermination (work point±hysteresis). For weighting the amplitudedetermined by circuit 25 and for determining the amount to becontributed by the amplitude for correcting the hysteresis, the speedand the signal frequency, respectively, attained in the meanwhile, aresignalled to the divider circuit 26 through a counter 27 and a pluralityof comparators 28 to 30. The counter 27, through a divider 31 reducingthe frequency of the cycle at the output of circuit 10 to 5 Hz, isactivated for half a cycle (10 ms). During that time, the counter 27according to FIG. 2 counts the positive flanks of the trigger outputsignal TA. The output signal of the counter 27, after completion of thecounting process, hence, is a measurement for the sensor frequency.

Once a lower speed threshold is reached, for example, in the start-up ofan automotive vehicle, which, according to FIG. 2, corresponds to asignal of 40 Hz., the first comparator 28 will supply to the dividercircuit 26 a corresponding signal. At this comparatively low vehiclespeed, measurement of the coupling factor k is considered to berelatively unreliable. The influence of the instantaneously measuredcoupling factor and of the corresponding amplitude, respectively, on thecorrection of the hysteresis is, therefore, maintained relatively low.Thus, when the input E2 is applied by comparator 28 (which only operatesat low vehicle speed), the influence of the coupling factor on thehysteresis is relatively low.

Reaching a higher speed results e.g. in a signal of 60 Hz. This will besignalled by the comparator 29 through the flip-flop and the OR-gate asshown, in a blocking of the signal provided by the comparator 28 and inthe actuation of the input E3 of the divider circuit 26. The couplingfactor k measured at the elevated speed is "safer" and its influence onthe hysteresis correction, consequently, higher than at the previouslydescribed lower speed resulting in a signal at the input E2. Thecomparator 30, at a still higher speed (120 Hz), generates the inputsignal E4. The coupling factor measured at that speed is weightedhighest.

Once a higher speed is attained, the hysteresis adjusted by the higherweighting, will be maintained even slower vehicle speed. A switch-backto the stage of lowest weighting will be made dependent on predeterminedevents, for example, on the actuation of the ignition. The described wayof weighting and restoring during switch-off of the ignition is, ofcourse, only one alternative among a number of capabilities.

The circuit configuration according to the present invention issubstantially less sensitive to noise signals because the sweep pointsand the hysteresis, respectively, of the trigger circuit no longer arerequired to be adjusted to the most unfavorable case--e.g. to thelargest air gap between sensor and toothed disc. The hysteresis,automatically, is raised and the response sensitivity is lowered,respectively, to such an extent as is permitted by the actual couplingfactor. Once the coupling factor is high, both the useful signals andthe (induced) noise signals are relatively high. However, throughraising the hysteresis, the response to such noise signals is precluded.If, conversely, the coupling factor is low, the useful signals willbecome weak; the response sensitivity of the trigger will become high.However, there will be no risk of mistriggering because the low couplingfactor will also weaken the noise signals. Hence, the technical advanceattained is substantial.

What is claimed is:
 1. A circuit configuration for processing outputsignals of a speed sensor of an automotive vehicle wheel to eliminatenoise from said output signals, said circuit configurationcomprising:first circuit means, responsive to: (a) output signals of aspeed sensor of an automotive vehicle wheel, and (b) previouslyprocessed output signals of said speed sensor,for developing: (a)average value signals representative of the average speed of saidautomotive vehicle wheel, and (b) coupling factor signals representativeof a coupling factor which is the amplitude of said output signalsdivided by the frequency of said output signals; second circuit means,responsive to: (a) said average value signals, and p1 (b) said couplingfactor signals,for generating control signals representative of theaverage speed of said automotive vehicle wheel and said coupling factor;and means responsive to said output signals of said speed sensor andsaid control signals for modifying said output signals by said controlsignals to develop said processed output signals.
 2. A circuitconfiguration in accordance with claim 1 wherein said first circuitmeans includes means for:(a) establishing a plurality of predeterminedfrequency ranges, (b) determining which of said frequency ranges thefrequency of said output signals fall into, and (c) weighting theinfluence of said coupling factor signals on said control signals basedon which of said frequency ranges the frequency of said output signalsfall into.
 3. A circuit configuration in accordance with claim 2,wherein said means for weighting the influence of said coupling factorsignals on said control signals include means for increasing theinfluence of said coupling factor with increasing frequency of saidoutput signals.
 4. A circuit configuration in accordance with claim 3,wherein said means for increasing the influence of said coupling factorwith increasing frequency of said output signals remain active untilactuation of a regularly recurring event.
 5. A circuit configuration inaccordance with claim 4, wherein said regularly recurring event isactuation of an ignition.
 6. A circuit configuration in accordance withclaim 1, wherein:said output signals include a signal representative ofa predetermined lowest speed having a corresponding amplitude and saidcircuit configuration further includes means for adjusting said couplingfactor signals to said amplitude corresponding to said signalrepresentative of said predetermined lowest speed.
 7. A circuitconfiguration for processing output signals of a speed sensor of anautomotive vehicle wheel to eliminate noise from said output signals,said circuit configuration comprising:first circuit means, responsiveto: (a) output signals of a speed sensor of an automotive vehicle wheel,and (b) previously processed output signals of said speed sensor,fordeveloping: (a) average value signals representative of the averagespeed of said automotive vehicle wheel, and (b) coupling factor signalsrepresentative of a coupling factor which is the amplitude of saidoutput signals divided by the frequency of said output signals; secondcircuit means, responsive to said coupling factor signals, fordeveloping hysteresis signals representative of a hysteresis which isincreasingly weighted by said coupling factor with increasing frequencyof said output signals; third circuit means, responsive to: (a) saidaverage value signals, and (b) said hysteresis signals,for generatingcontrol signals representative of the average speed of said automotivevehicle wheel and said hysteresis; and means responsive to said outputsignals of said speed sensor and said control signals for developingsaid processed output signals.
 8. A circuit configuration in accordancewith claim 7, wherein:said output signals include a signalrepresentative of a predetermined lowest speed having a correspondingamplitude and said circuit configuration further includes means foradjusting said hysteresis signals to said amplitude corresponding tosaid signal representative of said predetermined lowest speed.